[luci-go] remove isolate.sha1

isolate is taken from CIPD now

Change-Id: I6fb13fd6ae4bfda4ab9d414284c37cfc2dfc0e91
Reviewed-on: https://chromium-review.googlesource.com/c/1475144
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Marc-Antoine Ruel <maruel@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632600}
4 files changed